Stability and charge transfer of C3B ordered structures

Optimal balance: alkali metal-doped boron carbide nanosheets achieve superior stability and nonlinear optical responsiveness

Nonlinear optical (NLO) materials play a vital role in various technological domains, including optoelectronics and photonic devices. Designing NLO materials, particularly inorganic ones, that strike a compromise between nonlinear optical sensitivity and stability has always been a difficult task. In order to improve the stability and NLO responsiveness, we propose and examine alkali metal-doped boron carbide nanosheets (M@BCNs) in this study. Calculated interaction energies (E int), which span from -65.5 to -94.9 kcal mol-1, show the stability of the M@BCN complexes. The first hyperpolarizability value has also increased, to a maximum of 3.11 × 105 au, indicating improved nonlinear optical characteristics. QTAIM (quantum theory of atoms in molecules) and NCI (non-covalent interactions) analyses demonstrate the validity of the interactions. According to NBO (natural bond orbital) analysis, the alkali metals gain almost +1 charge. Due to the low transition energies and considerable charge transfer between the alkali metals and nanosheet, the nonlinear optical response is significantly improved. The M@BCN complexes also show transparency in the ultraviolet region, with absorption maxima ranging from 917 to 2788 nm. This study proposes a viable approach for developing alkali metal-doped boron carbide nanosheets with improved NLO response and stability.

Metal-organic framework derived crystalline nanocarbon for Fenton-like reaction

Nanoporous carbons with tailorable nanoscale texture and long-range ordered structure are promising candidates for energy, environmental and catalytic applications, while the current synthetic methods do not allow elaborate control of local structure. Here we report a salt-assisted strategy to obtain crystalline nanocarbon from direct carbonization of metal-organic frameworks (MOFs). The crystalline product maintains a highly ordered two-dimensional (2D) stacking mode and substantially differs from the traditional weakly ordered patterns of nanoporous carbons upon high-temperature pyrolysis. The MOF-derived crystalline nanocarbon (MCC) comes with a high level of nitrogen and oxygen terminating the 2D layers and shows an impressive performance as a carbocatalyst in Fenton-like reaction for water purification. The successful preparation of MCC illustrates the possibility to discover other crystalline heteroatom-doped carbon phases starting from correctly designed organic precursors and appropriate templating reactions.

Structural Characterization of Graphite Analogue BCx Synthesized Under Various Conditions and Its Application to Ti Intercalation

A graphite-like material boron carbide (BCx) was synthesized under various heat treatment conditions and extensively characterized. First, we synthesized the BCx precursor phase by a single-step reaction using a mixed solution of BBr3 and C6H6. We confirmed that the precursor phase had a graphite-like structure with B-C chemical bonds, but its crystallinity was poor. To improve their crystallinity, we annealed the precursor sample at high temperature using a high-frequency furnace and determined the annealing condition. We also investigated the magnetic properties of BCx. The high-temperature annealing for the precursor phase yields the highest Pauli paramagnetic susceptibility χPauli, indicating the highest density of states at the Fermi level. Accordingly, the high-temperature treatment for the precursor phase is significant to improve its crystallinity and physical properties. In addition, we synthesized a Ti-intercalated material TiBC by using the same procedure as that for making the BCx precursor phase. The crystal structure can be indexed by the AlB2 structure, indicating that Ti atoms are intercalated between the BC layers. The χPauli value of TiBC is obtained to be 1 order of magnitude smaller than that of BCx, suggesting the compensation of hole carriers by electron doping through Ti intercalation into the BCx system.

Analysis of 2D nanomaterial BC3 for COVID-19 biomarker ethyl butyrate sensor

Ethyl butyrate (EB) was identified in recent research as a prominent biomarker of COVID-19, as concentrations of EB were higher in exhaled breath of COVID-19 patients. Electronic sensitivities of pristine, Al- and Si-doped BC₃ nanosheets to the EB molecule were investigated in this study using density functional theory. It is found that the pure BC₃ was ineffective in sensing EB due to low adsorption energy and sensitivity. Aluminum- and silicon-doped BC₃ nanosheets were effective in forming a strong interaction with EB and were also sensitive. Our calculations show that the band gaps of the Al-doped and Si-doped BC₃ sheets were significantly decreased upon EB adsorption, which increased the electrical conductance of the sheets and the sensitivity. However, Si-doped BC₃ had a recovery time of almost 22 hours, making it less potent than Al-doped BC₃, which had a recovery time of just 7.7 minutes. The shorter recovery time of the Al-doped BC₃ sheet is due to its moderate adsorption energy of 25.8 kcal mol^-1. These results can help facilitate the development of an EB biosensor for COVID-19 testing and other similar applications.

Transition-metal single atoms embedded into defective BC3 as efficient electrocatalysts for oxygen evolution and reduction reactions

Searching for high-activity, stable and low-cost catalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of significant importance to the development of renewable energy technologies. By using the computational screening method based on the density functional theory (DFT), we have systematically studied a wide range of transition metal (TM) atoms doped a defective BC3 monolayer (B atom vacancy VB and C atom vacancy VC), denoted as TM@VB and TM@VC (TM = Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt), as efficient single atom catalysts for OER and ORR. The calculated results show that all the considered TM atoms can tightly bind with the defective BC3 monolayers to prevent the atomically dispersed atoms from clustering. The interaction strength between intermediates (HO*, O* and HOO*) and catalyst govern the catalytic activities of OER and ORR, which has a direct correlation with the d-band center (εd) of the TM active site that can be tuned by adjusting TM atoms with various d electron numbers. For TM@VB catalysts, it was found that the best catalyst for OER is Co@VB with an overpotential ηOER of 0.43 V, followed by Rh@VB (ηOER = 0.49 V), while for ORR, Rh@VB exhibits the lowest overpotential ηORR of 0.40 V, followed by Pd@VB (ηORR = 0.45 V). For TM@VC catalysts, the best catalyst for OER is Ni@VC (ηOER = 0.47 V), followed by Pt@VC (ηOER = 0.53 V), and for ORR, Pd@VC exhibits the highest activity with ηORR of 0.45 V. The results suggest that the high activity of the newly predicted well dispersed Rh@VB SAC is comparable to that of noble metal oxide benchmark catalysts for both OER and ORR. Importantly, Rh@VB may remain stable against dissolution at pH = 0 condition. The high energy barrier prevents the isolated Rh atom from clustering and ab initio molecule dynamic simulation (AIMD) result suggests that Rh@VB can remain stable under 300 K, indicating its kinetic stability. Our findings highlight a novel family of efficient and stable SAC based on carbon material, which offer a useful guideline to screen the metal active site for catalyst designation.

Adsorption of chloroquine and hydroxychloroquine as potential drugs for SARS-CoV-2 infection on BC3 nanosheets: a DFT study

The adsorption of HCQ on BC3 nanosheets is stronger than that of CQ. The hydrogenated BC3 nanosheet is a more prominent nanocarrier for the CQ and HCQ drugs than the bare BC3 monolayer.

Graphene-like boron carbide monolayer as an electronic and work function-type sensor for dopamine drug

The electronic response of both pristine and Al-doped BC₃ nanosheets toward 3, 4-dihydroxyphenyl ethylamine, i.e. dopamine (DA) was studied through density functional theory. Based on the adsorption energy the tendency of pristine BC₃ toward DA drug insignificant and also after adsorption of DA drug the electronic properties of BC₃ were changed negligibly. While doping the sheet by Al significantly increases its reactivity and sensitivity toward the DA drug. By adsorption of DA HOMO-LUMO gap dramatically decreased of from 1.34 to 1.12 eV, thereby enhancing the electrical conductivity. It indicates that the doped BC₃ nanosheets may be a suitable candidate as a DA electronic sensor, unlike the pristine BC₃. Furthermore, the work function of doped BC₃ was changed significantly after DA adsorption. Based on these results the doped BC₃ can also act as a work function-type sensor to the sensing of DA was used. Finally, the most important factor of the doped BC₃ sheet is a short recovery time of 7.36 ms for the desorption process of DA.

Staging Phenomena in Lithium-Intercalated Boron-Carbon

Hole-doped LiBC has become of great interest as a candidate for high-temperature superconductivity with its structural similarity to MgB₂ and as a possible cathode for rechargeable lithium batteries with the large graphenelike BC hexagons. The limitation on synthesis studies has detracted from the structural and electronic properties and application studies of Li _xBC. Here, we present the successful synthesis of hole-doped Li_0.5BC and its structural and electronic characterization using detailed structural modeling based on a unique stage-2 Daumas-Hérold-type domain structure consistent with X-ray diffraction data. The strong intralayer motion of the guest Li island induces extraordinary structural properties, such as staging and staging disorder, which are confirmed by the compressibility results obtained from Li_0.85BC (anisotropic cell compressibility with B₀ ∼ 134 GPa) and Li_0.48BC (isotropic cell compressibility with B₀ ∼ 190 GPa). Li deficiency increases the conductivity; however, the temperature-dependent conductivity is dominated by the thermal excitation of carriers in a strongly disordered regime with well-defined localized states.

Functionalization of the pristine and stone-wales defected BC3 graphenes with pyrene

The functionalization of pristine and Stone-Wales defected BC3 nanosheets with a pyrene molecule was investigated using density functional theory. Frontier molecular analysis shows that the main interaction is π-π stacking, releasing energies in the range of 143.6 to 169.1 kJ mol(-1). We predicted that after the functionalization process, the electrical conductance of the pristine sheet may be increased. Also, it modifies the work function of the pristine sheet and, as a consequence, its field-emission current densities may significantly enhance. However, the pyrene functionalization results in little change in the electronic properties of the defected sheet.

With the same Clar formulas, do the two-dimensional sandwich nanostructures X-Cr-X (X = C4H, NC3 and BC3) behave similarly?

The "perturbation" effects (i.e. hyperconjugation, electronegativity, and conjugation) on the structural, electronic, and magnetic properties of three kinds of two-dimensional (2D) X-Cr-X (X = C4H, NC3 and BC3 monolayers) sandwich nanostructures were systematically investigated by means of spin-polarized density functional theory (DFT) computations. Although all these 2D sandwich systems energetically prefer the same structural pattern and are featured with the same Clar formulas, their electronic and magnetic properties are significantly influenced by the "perturbations". Especially, a very strong π conjugation through the vacant p orbital of the B atom in BC3 leads to its sandwich structure with antiferromagnetic and conducting characters, which are in stark contrast to the non-magnetic and semiconducting characters of C4H-Cr-C4H and NC3-Cr-NC3. These findings reveal that simple counting Clar formulas alone are insufficient to fully understand the electronic and magnetic properties of graphene-related materials, and more attention should be given to such "perturbation" effects.

Symmetry groups of single-wall nanotubes

This work investigates the symmetry properties of single-wall carbon nanotubes and their structural analogs, which are nanotubes consisting of different kinds of atoms. The symmetry group of a nanotube is studied by looking at symmetries and color fixing symmetries associated with a coloring of the tiling by hexagons in the Euclidean plane which, when rolled, gives rise to a geometric model of the nanotube. The approach is also applied to nanotubes with non-hexagonal symmetry arising from other isogonal tilings of the plane.

Direct detection of uric acid in body fluid samples by using boron doped graphite nano particles as the working electrode

Boron doped graphite nano particles were used as functioning elements for creation of electrodes for the detection of uric acid in biological samples. The electrode obtained in this manner was capable of oxidizing ascorbic acid at lower potentials. This provided a desirable solution to the interfering problem encountered in the detection of uric acid in biological samples caused by ascorbic acid. The detectable concentrations for uric acid ranged from 5.0 to 130 µM. The applicability of the electrode was experimentally demonstrated by the successful direct detection of uric acid in real urine samples.

Structural and electronic properties of hydrogen adsorptions on BC₃ sheet and graphene: a comparative study

We have systematically investigated the effect of hydrogen adsorption on a single BC₃ sheet as well as graphene using first-principles calculations. Specifically, a comparative study of the energetically favorable atomic configurations for both H-adsorbed BC₃ sheets and graphene at different hydrogen concentrations ranging from 1/32 to 4/32 ML and 1/8 to 1 ML was undertaken. The preferred hydrogen arrangement on the single BC₃ sheet and graphene was found to have the same property as that of the adsorbed H atoms on the neighboring C atoms on the opposite sides of the sheet. Moreover, at low coverage of H, the pattern of hydrogen adsorption on the BC₃ shows a proclivity toward formation on the same ring, contrasting their behavior on graphene where they tend to form the elongated zigzag chains instead. Lastly, both the hydrogenated BC₃ sheet and graphene exhibit alternation of semiconducting and metallic properties as the H concentration is increased. These results suggest the possibility of manipulating the bandgaps in a single BC₃ sheet and graphene by controlling the H concentrations on the BC₃ sheet and graphene.

Structural Modification in Carbon Nanotubes by Boron Incorporation

We have synthesized boron-incorporated carbon nanotubes (CNTs) by decomposition of ferrocene and xylene in a thermal chemical vapor deposition set up using boric acid as the boron source. Scanning and transmission electron microscopy studies of the synthesized CNT samples showed that there was deterioration in crystallinity and improvement in alignment of the CNTs as the boron content in precursor solution increased from 0% to 15%. Raman analysis of these samples showed a shift of ~7 cm(-1) in wave number to higher side and broadening of the G band with increasing boron concentration along with an increase in intensity of the G band. Furthermore, there was an increase in the intensity of the D band along with a decrease in its wave number position with increase in boron content. We speculate that these structural modifications in the morphology and microstructure of CNTs might be due to the charge transfer from boron to the graphite matrix, resulting in shortening of the carbon-carbon bonds.

Phonon dispersion curves of a BC3 honeycomb epitaxial sheet

The entire phonon-dispersion curves along the Gamma-M direction of a BC3 honeycomb sheet have been determined both experimentally and theoretically for the first time. Most of the observed curves agreed with the theoretical ones calculated on the basis of ab initio theory. From the stretching force constants of the nearest-neighbor C-C and B-C bonds, together with that of the B-B bond, we clarified the characteristic feature of the C-C and B-C bonds. From the experimental and theoretical results, we discussed the possibility of high T(c).

Adsorption, diffusion, and recombination of hydrogen on pure and boron-doped graphite surfaces

Boron inserted as impurity by substitution of carbon atoms in graphite is known to modify the reactivity of the surface in interaction with hydrogen. Boron induces a better H retention capability in graphite while it makes easier the recombination into molecular hydrogen under heating in thermal-desorption experimental conditions. It has already been calculated that boron modifies the electronic structure of the surface, which results in an increase of the adsorption energy for H. This result seems in good agreement with the better retention for H in doped graphite, but contradictory with the easier recombination observed. The aim of this work is to dismiss this contradiction by elucidating the modifications induced by boron in the recombination mechanism. We studied the diffusion of H on pure and boron-doped graphite in the density functional theory framework. We determined a diffusionlike mechanism leading to molecular hydrogen formation. Finally, we have shown the fundamental modifications induced by boron on the [0001] graphite surface reactivity. From these calculations it stands out that recombination is the result of desorption on pure graphite and diffusion on B-doped surfaces, while the activation energy for the rate limiting step is half reduced by boron. The results are compared to experimental observations. The connection between the cluster and periodic quantum modes for graphite is also discussed.